What bond links amino acids in a protein?

• A. Peptide bonds
• B. Ionic bonds
• C. Hydrogen bonds
• D. Phosphodiester bonds

Answer: (A)

The bond that links amino acids in a protein is a peptide bond, a covalent linkage formed when the carboxyl group of one amino acid reacts with the amino group of the next amino acid, releasing a water molecule in a dehydration synthesis. This connection creates the polypeptide backbone that forms proteins, and the peptide bond has partial double-bond character due to resonance, giving it planarity and limiting rotation around that bond. Ionic bonds occur between charged side chains and help stabilize interactions between distant parts of the molecule, not join amino acids in the sequence. Hydrogen bonds help stabilize secondary structures like alpha helices and beta sheets by linking different parts of the backbone, but they don’t fuse amino acids together in the chain. Phosphodiester bonds link nucleotides in nucleic acids, not amino acids in proteins. So the peptide bond is the essential link that fuses amino acids into a protein.